It is generally required to check that the volume of air issuing from grills of the air conditioning systems in buildings is balanced from grill to grill, i. e. that the same volume of air is issuing from each grill of the system. If this is not done, heating systems may be overworking and inefficient, which is environmentally undesirable. It may also be required to check other characteristics of the air issuing from such grills. In the past, airflow measuring hoods have been fabricated on a"suit the particular job"basis from cardboard. The cardboard is folded to the appropriate tapered funnel shape of a suitable size to match the grill concerned, and then fastened with adhesive tape. An anemometer is attached by adhesive tape to the downstream end of the hood to perform the measuring function. Such a hood is not collapsible, or reusable after dismantling, and in consequence tends to be discarded after a particular job is completed. It is a very time consuming operation to make such a hood for each job, and suitable pieces of cardboard are not always readily available. Such a hood is relatively heavy and is therefore difficult to use. In addition, the hood so constructed is usually not of a standard size or configuration, so that only comparative measurements from grill to grill can be made, not accurate absolute measurements that can be compared with tests done in other locations on other occasions. To overcome such problems, it is known to produce airflow measuring hoods of a standard and reusable type. Certain of these airflow measuring hoods are of a rigid material, and in consequence are not collapsible. The outlet end of the hood is attached to a measuring instrument. Hence, such hoods are bulky and cumbersome to transport between locations, and are very heavy in use. Alternative fabric hoods have a rigid rectangular frame at the grill end that is to be attached to a grill, and the other, flexible, end is stretched over the frame of an airflow measuring instrument. Rods at each corner of the structure stretch the fabric between the two ends of the hood to support the fabric in the uniformly divergent configuration. Dismantling and assembling such hoods by one person is relatively inconvenient. Such hoods are still bulky and cumbersome to transport. In either case, the instrument is matched to the hood and is programmed to compensate for differing flow rates and air properties, a built-in factoring calculation facility. Such a hood/instrument combination is expensive, and in consequence, many contractors are not prepared to obtain and use such equipment. In addition, the measuring instruments can only be used by skilled persons, and such persons may not always be readily available. Even if a system is balanced initially by the contractor, it may become unbalanced eventually, and maintenance personnel may not have the required equipment to remedy the imbalance or be sufficiently skilled in the use of such equipment. Furthermore, if more than one property of the airflow is to be measured, one or more instruments must be attached to the airflow measuring instrument, adding to the weight and complexity of the assembly in use.

It is an object of the present invention to provide an air capture device that avoids, at least to an appreciable extent, the disadvantages of the known hoods outlined above.

The invention provides an air capture device comprising a pair of frames, a support rod in use extending between and engaged with the frames and disengageable therefrom, a fabric shell having opposed edges secured to a respective one of the frames, and means adapted to secure a measuring instrument to one of the frames.

The frames may be rectangular, and may be square in planform. Each frame may have a cross member extending from opposed sides of the frame across the centre thereof. In this case, the support rod may extend in use between the centres of the two cross members.

Alternatively, two support rods may extend in use between the frame at an instrument end of the air capture device and a cross member extending from opposed sides of the frame at a grill end of the air capture device across the centre thereof. The ends of a support rod and the cross member or frame with which it connects may have co-operating formations thereon for mutual location. The co-operating formations may comprise a spigot and a recess adapted to receive a spigot therein. The frames, and the or each cross member and support rod may be of aluminium tubing, and may be of square cross-section. Alternatively, the frames, and the or each cross member and support rod, may be of a plastics material. The cross member at the instrument end of the air capture device may extend outwardly of the respective frame, and may have a handle attached at each end thereof. Each handle may be positional adjustable to extend in a selected direction in a plane perpendicular to the axis of the cross member. The selected direction may be one of four mutually perpendicular directions.

The frame at the grill end of the air capture device may have a gasket attached thereto. The frame at the grill end-may be of larger area than that at the instrument end, whereby the fabric shell converges from the grill end to the instrument end of the air capture device. The fabric shell may have a convergent section over a portion thereof and a constant cross-sectional area over the remainder thereof. The fabric shell may converge in the convergent section at an included angle of between 155° and 165°. The fabric shell may be a textile material coated to be impervious to air.

The instrument attachment means may comprise straps, which may comprise fastening means. The fastening means may be touch and close fastenings. The fabric shell may have a substantially transparent pocket therein through which an instrument contained therein may be viewed.

The air capture device may also comprise an insert having a plurality of vanes operable in use to divide the interior of the shell into separate air passageways. The insert may have a central sleeve adapted to receive the support rod therein. The insert may have four vanes and each vane may have means adapted to attach a free edge thereof to the shell. The insert may be of a textile fabric.

The invention may comprise an air capture device as aforesaid and a carrying means, which may be a bag. The bag may have a planform of the same size as the frame at the grill end of the air capture device. The length of the support rod is preferably not greater than the diagonal measurement of the frame at the grill end. The carrying means may have à pocket adapted to receive the support rod, and the pocket may extend between diagonally opposed corners of carrying means. The carrying means may have a handle attached thereto.

The invention will now be described with reference to the accompanying drawings in which Fig. 1 is a perspective view of a first embodiment of air capture device, Fig. 2 is a perspective view of an insert for the air capture device of Fig. 1, Fig. 3 is a perspective view of a second embodiment of air capture device, Fig. 4 is a scrap view to a larger scale of a support rod of the device of Fig. 3, and Fig. 5 is a perspective view of a carrying bag for the devices of Figs. 1 and 3.

Referring now to Fig, 1 there is shown an air capture device 10 comprising a pair of frames 11,12. The frames 11,12 are square in planform, but could be rectangular or any other appropriate shape depending on the grills in connection with which the air capture device 10 is to be used. Each frame 11,12 has a cross member 13 extending from opposed sides of the frame 11,12 across the centre of the frame 11,12. A support rod 14 in use extends between and is engaged with the frames 11,12. The support rod 14 has a spigot 15 at one end that is received in a recess in the centre of the respective cross member 13. At the other end of the support rod 14 and the other cross member 13, the spigot 15 and recess are reversed so that the two frames 11, 12 can clip together when the support rod 14 is removed and the air capture device 10 collapsed for storage or transportation. As an alternative, in order that there is no cross member 13 in the frame 12 to interfere with the flow of air in that region, two support rods 14a (only one is shown, in dashed lines for clarity) may be located between the frame 12 and the cross member 13 of the frame 11. A fabric shell 16 having its opposed edges secured to a respective one of the frames 11,12 is stretched between the frames 11, 12 when the support rod 14 is put in place. There is sufficient movement available in the fabric shell 16 that, by pulling the frames 11,12 apart, the support rod 14 may be disengaged from the cross members 13 for purposes of transportation and storage of the air capture device 10.

The frames 11,12, the cross members 13 and the support rod 14 are of aluminium tubing of square cross-section. A gasket 27 is attached to the frame 11 to allow for uneven ceilings and to provide protection for the device 10. The frame 11 at the grill end 17 of the air capture device 10 is of larger area than the frame 12 at the instrument end 18 thereof, whereby the fabric shell 16 converges from the grill end 17 to the instrument end 18 of the air capture device 10. The fabric shell 16 has a convergent section 19 over a portion thereof and a constant cross-sectional area over the remainder 20 thereof. The fabric shell 16 converges in the convergent section 19 at an included angle of between 155° and 165°. Alternatively, the fabric shell 16 may converge at a constant rate from the grill end 17 to the instrument end 18 if desired. The fabric shell 16 is of a textile material coated to be impervious to air. The fabric shell 16 is provided with a substantially transparent pocket 28 through which an instrument contained therein may be viewed.

The cross member 13 at the instrument end 18 of the air capture device 10 extends outwardly of the frame 12, and has a handle 21 attached at each end thereof. Each handle 21 is positional adjustable to extend in a selected direction in a plane perpendicular to the axis of the cross member 13, i. e. they can be positioned to extend vertically upwards, vertically downwards, horizontally in either direction, or at intermediate positions as desired depending on the location of the grill concerned and the accessibility of the handles 21.

Depending from the frame 12 are straps 22 to enable a measuring instrument, for example an anemometer, a pitot tube, an air sampler or a temperature probe, to be secured to the air capture device 10. The straps 22 are provided with touch and close fastenings 23, but other forms of fastening means may be provided if preferred, e. g. buckles.

In Fig. 2, there is shown an insert 29 for the air capture device 10 for use when the device 10 is being used with a swirl diffuser grill. In such a case, the air issuing from the grill travels in a swirling motion such that it is difficult to obtain representative readings on an instrument located at the instrument end 18 of the device 10. The insert 29 has a central sleeve 30 into which the support rod 14 is inserted. The four fabric"vanes"31 attached to the sleeve 30 are then attached to the inside of the shell 16 at either the middle of each side or the corners, as preferred, by means of the straps 32. These straps 32 have touch and close fastenings for this purpose. The insert 29 is located just below the frame 11, and extends to the bottom of the convergent section 19. The insert 29 has the effect of reducing the swirling of the air by the time it reaches the instrument end 18 of the devices 10,40, thereby enabling a more accurate measurement to be taken than would otherwise be the case.

Referring now to Fig. 3 there is shown an air capture device 40, which is similar in most respects to the air capture device 10, and corresponding parts are identified by the same numerals. In this embodiment however, there are no cross members 13 so that the interference with the airflow through the air capture device 40 is minimise. Instead, the frames 11,12 are maintained for use of the air capture device 40 by means of a pair of support rods 41. The support rods 41 engage the frames 11,12 by means of spigots 15 and recesses as described above. Gaskets 27 are provided on both frames 11, 12. In this case, an anemometer 42 is mounted on a removable bracket 43 attached to frame 12 at the instrument end 18 of the air capture device 40.

As shown more clearly in Fig. 4, the support rods 41 are formed in two parts 43,44. Each part 43,44 is a tubular. One part 43 has a elongate attachment pin 45 provided on one end, the attachment pin 45 being received within the end of the other part 44. A coil spring 46, of free length shorter than the attachment pin 45, is mounted on the attachment pin 45. The length of spring 46 is preferably approximately half that of the attachment pin 45. This arrangement enables the assembled support rods 41 to be shortened for engagement with or disengagement from the frames 11,12, whilst maintaining tension in the fabric shell 16 when the air capture device 40 is in use.

Referring now to Fig. 5, there is shown a carrying bag 24 for the air capture device 10 of Fig.

1 or air capture device 40 of Fig. 3. The bag 24 has a planform of the same size as the frame 11 of the air capture devices 10,40 so that, when the support rod 13 is, or rods 41 are, removed and the air capture devices 10,40 collapsed, the bag 24 can receive both frames 11, 12 and the fabric shell 16. The length of the support rod 14 is not greater than the diagonal measurement of the frame 11, and support rods 41 can be separated into their component parts 43,44. For this purpose, the bag 24 has a pocket 25 adapted to receive the support rod 13 or support rods 41, the pocket 25 extending between diagonally opposed corners of carrying bag 24. The carrying bag 24 has a handle 26 attached thereto. As an alternative, the bag 24 may be deeper to accommodate a set of three or other number of air capture devices 10,40.

By means of the invention an air capture device is provided that is relatively inexpensive, and can therefore readily be obtained and used by all contractors and maintenance personnel.

Assembly and dismantling of air capture devices 10,40 is simple, quick, and easily performed by one person. The air capture devices 10,40 are lightweight in use and for transportation, and the adjustable handles 21 enable convenient use in any location. The air capture devices 10,40 can be used for all air measurements by attachment of an appropriate instrument to the instrument end, and since careful calibration is not required, the devices 10,40 can be used by less skilled persons than is the case with the hoods with instrumentation matched to the hood for factoring calculation purposes.